The polyphase AC motor, particularly a permanent magnet synchronous motor is extended in the range of applicable uses to household electric appliances, industries, motorcars, etc. by utilizing the characteristics such as a small size and high efficiency. Particularly in recent years, electric motors having a driving system changed from the square wave power supply type to the sine wave power supply type are increased and controllers requiring the input of electric constant set values of an electric motor such as resistance, inductance, and induced voltage constant for uses of rotor position inference under the position sensorless control and high precision torque control are increased. Therefore, unless the electric constants of the electric motor are identified and input accurately, the control performance is greatly affected. Among them, particularly the inductance is greatly affected by the magnetic nonlinearity of the core and is very dependent upon the magnetic saturation.
Under such a condition, aiming to realize miniaturization and cut-down of cost of the electric motor, for example, as disclosed in Patent Literature 1, a claw-teeth type motor composed of a stator of a circular claw magnetic core formed with a dust core and a rotor arranged in the ring of the stator is developed. However, as described even in Patent Literature 1, the claw-teeth type motor, since the stators having three independent phases are overlaid by each other in the axial direction, is smaller in the magnetic resistance of the intermediate phase than other phases and has a three-phase unbalanced property in principle. Therefore, magnetic flux pulsations of a secondary electric angle (two cycles per each cycle of the electric angle) are generated and furthermore, torque pulsations of the same order are caused.
Arts for reducing the magnetic flux pulsations and torque pulsations of the claw-teeth type motor are disclosed in Patent Literature 1 and Patent Literature 2.
Firstly, Patent Literature 1 discloses an art, from the structure that the individual phases are adjacent to each other in the axial direction, for balancing the magnetic resistance of the claw-teeth type motor of three-phase unbalance by inserting a magnetic insulating material composed of a non-magnetic substance between the phases. A characteristic of the claw-teeth type motor is a structure that the stators of three independent phases are adjacent to each other in the axial direction, thus the magnetic resistance of the intermediate phase is small, and three-phase unbalance is caused. Therefore, the prior art 1 inserts a magnetic insulating material between the phases, thereby realizes magnetic insulation, balances the three phases, thereby reduces the magnetic flux pulsations of the secondary electric angle, furthermore the torque pulsations of the same order.
Further, in Patent Literature 2, an art of calculating the torque pulsations beforehand by a torque pulsation calculating means, adding the waveform of the opposite phase from the calculated torque pulsation component to the command value, and reducing the pulsation component is disclosed. In the prior art 2, the pulsation characteristic is obtained beforehand using the torque pulsation calculating means of the electric motor, and it is added to a torque pulsation command at the time of driving, thus the torque pulsations are reduced.